Combustible gas detector



Feb. 12, E957 M. PISANO COMBUSTIBLE GAS DETECTOR Filed May 18, 1953 All? FL UW INVENTOR- Zfi/ ATT H/VEY.

United States Patent F This invention relates to an improved combustible gas alarm of the type employing a thermocouple in conjunction with companion, heated catalyst coils housed by suitable chambers therefor.

As a salient objective, the invention is especially directed to the provision of a reliable device of low cost and simplicity of construction and operation, and adapted for use in mines, shops, and miscellaneous commercial establishments as well as homes and garages for indicating the presence of combustible gases in air-gas mixtures below a lower explosive limit, or warning of the presence of the highly toxic and combustible gas carbon monoxide.

Heretofore, in certain devices of the type indicated, the catalyst coil has been housed in a combustion chamber through which the air-gas mixture to be sampled is caused to flow. Difficulty, with varying results, has been experienced, however, through the fact that when the ratio of combustible gas in the air-gas mixture exceeds a certain percentage, or is high, the catalyst coil becomes devitalized and temporarily ceases to function accurately, or is subject even to permanent failure.

To obviate the difficulty noted, it has been proposed, in some instances, to employ intermittent surges of heating current through the coil for revitalizing the coil. In other instances, it has been proposed to dilute the sampled air-gas mixture with an excess of air, so as to maintain the ratio of combustible gas in the mixture at a low level. In still other instances, additional air has been forced through the combustion chamber, but this procedure is subject to its own diificulty in that the air-gas content of the mixture in contact with the catalyst coil is not uniform. In still other instances, advantage has been taken of the draft induced through the combustion chamber by the heated coil therein for accelerating the flow of the mixture through said chamber.

It has been discovered, however, that if the velocity of the mixture flowing through the combustion chamber is increased immediately at the zone of the catalyst coil therein, while at the same time the normal pressure of the mixture in said zone is lowered, the so-called poisoning or contamination of the coil is greatly discouraged, or retarded, while, also, the character of the mixture remains uniform.

It is therefore a further object of the invention to provide a device wherein the velocity of flow of the air-gas mixture through the combustion chamber of the device will be accelerated immediately at the zone of the catalyst coil therein, while, also, the normal pressure of the mixture in said zone will be concurrently decreased, whereby the dependability of the device will be greatly enhanced.

Other and incidental objects will appear as the description of the invention proceeds.

The figure of the drawings is a diagrammatic view of my improved alarm, parts being shown in section.

In carrying the invention into effect, I employ a combustion chamber 10 flared at its ends and provided with an elongated throat 11 of uniform diameter, said chamber being in the form of a venturi tube. Overlying the ends 2,781,249 Patented Feb. 12, 1957 of the chamber are flame arresters 12. A suitable screen of 40 mesh with about 35% free opening will sufiice for each. In conjunction with the chamber 10, I further provide a cylindrical reference chamber 13 closed at its ends. This chamber contains plain air.

Extending at its ends into the chambers 10 and 13 is a thermocouple unit 14, and surrounding the ends of said unit are identical catalytic coils 15 and 16 respec tively of bare platinum ribbon. The thermocouple unit preferably includes a plurality of suitable series-connected thermocouple junctions positioned within each coil.

Power is supplied from a suitable source through an appropriate transformer 17, and connecting the coils 15 and 16 in parallel in a heating circuit are wires 18 and 19. Interposed in'the heating circuit is a balancing rheostat 20 for the coils, and, preferably, a main switch 21 is provided for rendering the device inoperative when so desired. Connected across the heating circuit is a green pilot light 22 adapted to indicate the presence of supply power when the main switch is closed.

A relay of appropriate character is indicated at 23. .This relay includes a knob 24 by means of which the relay may be manually reset, and connecting the relay across the heating circuit to provide a relay circuit are Wires 25, 26, and 27. Interposed in the relay circuit is a suitable alarm buzzer 28, .and connected across said circuit is a red alarm light 29. Connecting the thermocouple unit 14 with the relay 23 are Wires 30 and 31 providing a thermocouple circuit.

In an alarm of the present character, the ability to indicate potential explosive hazards well below a lower explosive limit is important, so that, in the event of an accumulation of gas or vapor, suflicient time will remain to take corrective measures. Thus, sensitivity of the device becomes of prime consideration. This qualification may be accomplished through the use of a maximum number of series thermocouples that can be inserted within the two catalyst coils 15 and 16 to provide a correspondingly strong potential in the thermocouple circuit for triggering the relay 23.

Normally, the coils 15 and 16 will be at temperature levels of from 1200 F. to 1400 F., and, initially, the

balancing rheostat 20 is actuated to produce equal coil temperatures under nil conditions, as registered by the thermocouple circuit and relay 23. Under such conditions, the voltage produced by the thermocouples will be zero.

Subsequent to adjustment, the presence of combustible gases in the combustion chamber 10 will cause direct burning to occur on the heated surface of the coil 15, thereby augmenting the surface temperature of the coil, while the coil 16 in the reference chamber 13 will remain unaffected. As will be appreciated, this thermal unbalance will result in a thermocouple voltage directly proportional to the quantity of the combustible gas present, and at given or arbitrarily set low limit of gas concentration, the relay 23 will be triggered, with the result that the alarm buzzer 28 will be caused to sound while the red alarm light 29 will be simultaneously energized.

It is now to be noted that the catalytic coil 15 is located in the throat 11 of the chamber 10, and, of course, the heat generated by the coil will produce an upward draft through the chamber of the air-gas mixture being sampled. Due to the shape of the chamber, however, the velocity of the rising current of the mixture will be increased at said throat while the normal pressure of the mixture will be decreased immediately at the zone of the coil 15. As a result, any tendency of the coil to become devitalized when subjected to high gas ratio of the air-gas mixture will be retarded without diluting the mixture with additional air. The device will thus be rendered correspondingly more accurate and dependable in practical use.

Having thus described my invention, I claim:

In an apparatus for analyzing air for the presence of a combustible gas therein, the combination of a closed reference chamber, a separate tubularcombustion chamber arranged in spaced relation adjacent said reference chamber and disposed for the flow therethroughof a current of air to be analyzed, a thermocouple unit extending between said chambers and having angularly disposed end portions projecting into corresponding ends of said chambers, the angular end portions of said uni-t each comprising a plurality of series-connected thermocouple junctions, a companion catalyst coils encircling the angular end portions of said unit about said junctions, and a heating circuit connecting said coils parallel, said combustion chamber having flared ends connected by an elongated throat at the zone of the coil in said combustion chamber for accelerating the velocity of said current of air through said zone and simultaneously reducing the normal pressure of the air in said zone about the coil therein.

UNITED STATES PATENTS Lamb et a1. May 16, Potter Feb. 7, Morgan June 8, Price Apr. 19, Guaragna Mar. 9, Jacobson June 12, Jacobson et a1 J an. 15, M cEvo y Sept. 15,

FOREIGN PATENTS Great Britain Oct. 25, France Sept. 30,

Addition to 937,257 France Jan. 29, 

